This invention relates to the preparation of oxybisphthalic compounds, and more particularly to their preparation by an improved phase transfer catalysis method.
Oxybisphthalimides and oxybis(phthalic anhydrides) are intermediates for the preparation of polyetherimides. The oxybisphthalimides have, in some instances, been easier to prepare than the oxybis(phthalic anhydrides) and can subsequently be converted thereto by hydrolysis and dehydration. It is also possible, however, to prepare oxybis(phthalic anhydrides) directly.
As disclosed in U.S. Pat. No. 4,780,544, the oxybisphthalimides have been prepared by the reaction of a nitro-substituted phthalimide with an alkali metal carboxylate such as potassium acetate in a dipolar aprotic solvent such as dimethylformamide or dimethyl sulfoxide. More conveniently, U.S. Pat. No. 4,933,469 describes their preparation in a non-polar organic solvent, preferably in the presence of a phase transfer catalyst. Reaction temperatures are in the range of about 100-4000.degree.C., most often about 150-200.degree. C. Yields above 70% are obtained with a dialkylaminopyridinium salt as phase transfer catalyst only when the solvent is distilled through calcium hydride to remove water; similar yields can also be obtained by the catalytic use of tetraphenylphosphonium bromide, a very expensive compound. U.S. Pat. No. 4,808,731 discloses the preparation of oxybis(phthalic anhydrides) by a simple condensation of a nitro- or fluoro-substituted phthalic anhydride (not requiring carboxylate), also in the presence of a dialkylaminopyridine, but disclosed yields are no higher than 57%.
A method similar to that of the aforementioned patents but using, for example, alkali metal carbonates instead of carboxylates is also known. U.S. Pat. No. 4,946,985 discloses such a method in which the carbonate is used in combination with water. According to U.S. Pat. No. 5,153,335, the reaction is more effectively conducted in the absence of water and employs a benzoic acid such as 4-chlorobenzoic acid as a catalyst.
U.S. Pat. No. 5,132,423 discloses the use of substituted guanidinium salts as phase transfer catalysts for nucleophilic aromatic substitution reactions such as the reaction of bisphenol A salts with halo- or nitro-substituted phthalimides to yield bis(phthalimides). It is not clear therefrom, however, whether the reaction between a substituted phthalic compound and a carboxylate or carbonate salt is chemically similar.